linux-kernel - Re: [PATCH 1/3] powerpc/numa: Set numa

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Date:   Fri, 13 Mar 2020 12:38:45 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Joonsoo Kim <js1304@...il.com>
Cc:     Sachin Sant <sachinp@...ux.vnet.ibm.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Christopher Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus

On 3/13/20 12:04 PM, Srikar Dronamraju wrote:
>> I lost all the memory about it. :)
>> Anyway, how about this?
>> 
>> 1. make node_present_pages() safer
>> static inline node_present_pages(nid)
>> {
>> if (!node_online(nid)) return 0;
>> return (NODE_DATA(nid)->node_present_pages);
>> }
>> 
> 
> Yes this would help.

Looks good, yeah.

>> 2. make node_to_mem_node() safer for all cases
>> In ppc arch's mem_topology_setup(void)
>> for_each_present_cpu(cpu) {
>>  numa_setup_cpu(cpu);
>>  mem_node = node_to_mem_node(numa_mem_id());
>>  if (!node_present_pages(mem_node)) {
>>   _node_numa_mem_[numa_mem_id()] = first_online_node;
>>  }
>> }
>> 
> 
> But here as discussed above, we miss the case of possible but not present nodes.
> For such nodes, the above change may not update, resulting in they still
> having 0. And node 0 can be only possible but not present.

So is there other way to do the setup so that node_to_mem_node() returns an
online+present node when called for any possible node?